This invention relates generally to process instruments used in industrial process control systems. More particularly, the present invention relates to process transmitters having inclination measurement sensors.
Process transmitters are used to remotely monitor a process variable, such as pressure, temperature or flow, of a process fluid, such as a petrochemical or water. A process transmitter typically includes a sensor or transducer that produces an electrical signal in response to physical changes in a process variable. For example, capacitive pressure transducers or piezoresistive pressure transducers produce an electrical signal as a function of the pressure of a process fluid. The sensor signal is processed by transmitter circuitry to produce an output signal that can be monitored as an indication of a process variable of the process fluid. The output signal can be monitored remotely at a control room such as through a control loop or network, or can be monitored locally such as with an LCD screen.
In order to couple the circuitry and the sensor with the process fluid, the components are contained in a housing that can be mounted to a process fluid vessel, such as a storage tank or pipeline, with process connections such as flanges, manifolds, diaphragms or other coupling devices. Various combinations of process connections allow the transmitters to be mounted in a variety of orientations for different applications, to overcome physical barriers and for customer preferences.
In pressure transmitters, for example, a pressure sensor is mechanically coupled with the process fluid through a mounting flange comprising a flexible diaphragm that isolates the sensor of the pressure transmitter from the process fluid. The diaphragm is linked with the pressure sensor through passageways that are filled with a substantially incompressible fill fluid. As the process fluid presses against the diaphragm, the fill fluid conveys the pressure to the pressure sensor, wherein the pressure reading is determined. The fill fluid itself also exerts a force on the pressure sensor due to its own weight, for which the transmitter must be calibrated. Changing the orientation of the transmitter can affect the amount of this force due to what is known as head effect. Typically, for lower pressure applications, an operator is required to perform a recalibration after the transmitter has been installed in a new orientation to reset the zero pressure reference orientation.
Additionally, after reorienting a transmitter, such as for a new application or a changed process vessel, the process transmitter may be positioned in such a manner that the LCD display is awkwardly positioned, therefore making it difficult for a user to read the display. In order to reconfigure the LCD display it must be removed from the transmitter housing and reinstalled, typically in 90-degree increments. As such, it would be desirable to eliminate or otherwise reduce inconveniences related to reorienting process transmitters.